1. Field of the Invention
The present invention relates to a position control apparatus and position control method of an optical system that irradiates converging light on an optical storage medium and to a storage and reproduction apparatus that irradiates a converging light beam on an optical storage medium and stores or reproduction information.
2. Descriptions of the Related Art
As optical apparatuses, for example, there are apparatuses that record or reproduction information using optical disks and other optical recording media, optical microscopes, etc.
In an optical apparatus, a cutoff spacial frequency fc is generally expressed by the following equation (1), using the numerical aperture NA of an objective lens and the wavelength xcex of the emitting light of a light source.
fc=2NA/xcexxe2x80x83xe2x80x83(1)
The shorter the wavelength xcex of the light from the light source or the greater the numerical aperture NA of the objective lens, the higher the resolving power thereof, thus enabling recording at high density using a storage and reproduction apparatus and the more detailed the observations using an optical microscope.
As a method of increasing the numerical aperture NA of an objective lens, there is known a near-field optical system employing a solid immersion lens (SIL). With this method, an optical system having a numerical aperture exceeding 1 has been achieved.
As a reference on near-field optical systems and solid immersion lenses, there is S. M. Mansfield, W. R. Studenmund, G. S. Kino, and K. Osato, xe2x80x9cHigh-numerical-aperture lens system for optical storagexe2x80x9d, Opt. Lett. 18, pp.305-307 (1993) (hereinafter referred to as xe2x80x9creference 1xe2x80x9d).
In addition, as another reference, there is H. J. Mamin, B. D. Terris, and D. Rugar, xe2x80x9cNear-field optical data storagexe2x80x9d, Appl. Phys. Lett. 68, pp.141-143 (1996) (hereinafter referred to as xe2x80x9creference 2xe2x80x9d).
In the above reference 1, as shown in FIG. 11A, laser light converged by an objective lens 101 strike the spherical incidence surface of the solid immersion lens 102 and is emitted from the flat emission surface of the solid immersion lens 102.
At this time, because the laser light from the objective lens 101 perpendicularly strikes the spherical incidence surface of the solid immersion lens 102, this light is converged at the center of the emission surface of the solid immersion lens 102.
In this way, if the refractive index of the solid immersion lens 102 is n, the numerical aperture of the objective lens 101 can be substantially enlarged n-fold.
Japanese Unexamined Patent Publication (Kokai) No. 8-212579 discloses an optical apparatus employing the aforesaid near-field.
This optical apparatus comprises a first lens holder for holding an objective lens and a second lens holder for holding a solid immersion lens. The first lens holder and the second lens holder are driven by a first actuator and a second actuator, respectively, and move in the focus direction.
In addition, focus control is performed by controlling the first actuator on the basis of the electrostatic capacitance formed by the solid immersion lens and between a conductive material and an optical disk. The distance between the solid immersion lens and the optical disk is maintained in a certain range.
However, in the optical apparatus disclosed in the aforesaid Japanese Unexamined Patent Publication (Kokai) No. 8-212579, because two actuators are used for focus control, there are the problems that the optical head ends up becoming heavy and large in size while and the positioning accuracy of the optical head declines.
In addition, in this optical apparatus, there is the problem that electrical and mechanical interferences between actuators easily occur and the precision of focus control is low.
In addition, this publication has no descriptions about the mechanism and control for causing the lens to move in the tracking direction and in the direction of the signal string on the optical storage medium.
A first object of the present invention is to provide a position control apparatus of an optical system and a position control method of an optical system and a storage and reproduction apparatus which are able to reduce the weight and size of the optical head when a near-field optical system employing a solid immersion lens is adopted.
In addition, a second object of the present invention is to provide a position control apparatus of an optical system and a position control method of an optical system and a storage and reproduction apparatus which are able to achieve high precision focus control when the aforesaid near-field optical system is adopted.
In addition, a third object of the present invention is to provide a position control apparatus of an optical system and a position control method of an optical system and a storage and reproduction apparatus which are able to make a lens move in a tracking direction and a signal string direction on an optical storage medium when the aforesaid near-field optical system is adopted.
In order to solve the above problems of the related art and achieve the above object, the position control apparatus of an optical system of a first aspect of the present invention comprises an optical system forming a near-field with an optical storage medium and irradiating a converging light beam to the optical storage medium, wherein an objective lens converging the light beam to be irradiated on the optical storage medium and a solid immersion lens with an electrode formed on a surface facing the optical storage medium and irradiating the light beam converged by the objective lens to the optical storage medium are fixed by a holding means, an actuator for moving the holding means in the focus direction perpendicularly intersecting the storage surface of the optical storage medium, and a control circuit for controlling the actuator on the basis of electrostatic capacitance formed by the electrode and the optical storage medium and of a reflected light from the optical storage medium so that the distance between the solid immersion lens and the optical storage medium becomes within the region where the near-field is formed.
The functions of the position control apparatus of an optical system according to the first aspect of the present invention are as follows.
The holding means in the optical system is placed at a specific position in the focus direction.
Here, there arises electrostatic capacitance between the optical storage medium and the electrode formed on the solid immersion lens.
In addition, in the optical system, the light emitted from a specific light source is emitted to the optical storage medium through the solid immersion lens after being focused by the objective lens. This light is reflected by the optical storage medium.
In the control circuit, the actuator is controlled on the basis of electrostatic capacitance formed by the electrode and the optical storage medium and of the reflected light from the optical storage medium. The distance between the solid immersion lens and the optical storage medium is adjusted so as to be within the region where the near-field is formed.
In this position control apparatus of an optical system, the objective lens and the solid immersion lens are fixed by a holding means. The holding means is moved by the actuator.
Therefore, compared with the optical apparatus described previously, the number of actuators can be decreased, the influence due to the interference between actuators can be reduced, and an optical head of reduced size and weight is achievable. Consequently, it becomes possible to position the objective lens and the solid immersion lens in the focus direction at a high precision.
In addition, in the position control apparatus of an optical system according to the first aspect of the present invention, preferably the numerical aperture of the optical system is greater than 1 and not greater than 3, the region where the near-field is formed is in a contactless state with the optical system and optical storage medium, the distance is in the range no more than 500 nm.
In addition, the position control apparatus of an optical system according to the first aspect of the present invention preferably further comprises a moving means for moving an optical head carrying at least the optical system, the first actuator, and the second actuator in the radial direction of the optical storage medium.
In addition, a position control apparatus of an optical system according to a second aspect of the present invention comprises an optical system forming a near-field with an optical storage medium and irradiating a converging light beam to the optical storage medium, wherein an objective lens converging the light beam to be irradiated to the optical storage medium and a solid immersion lens with an electrode formed on a surface facing the optical storage medium and irradiating the light beam converged by the objective lens to the optical storage medium are fixed by a holding means, a first actuator for moving the holding means in the focus direction perpendicularly intersecting the storage surface of the optical storage medium, a second actuator for moving the holding means in the radial direction of the optical storage medium, a first control circuit for controlling the first actuator on the basis of electrostatic capacitance formed by the electrode and the optical storage medium and of a reflected light from the optical storage medium so that the distance between the solid immersion lens and the optical storage medium is within the region where the near-field is formed, and a second control circuit for controlling the second actuator on the basis of the reflected light from the optical storage medium.
In addition, in the position control apparatus of an optical system according to the second aspect of the present invention, preferably, the second control circuit controls the second actuator on the basis of the reflected light of the optical storage medium, so that tracking control is performed based on at least one of a guiding channel existing on said optical storage medium, an emboss pit and a storage mark.
In addition, in the position control apparatus of an optical system according to the second aspect of the present invention, preferably the second control circuit generates a tracking error signal using any method among a push-pull method, 3-spot method, differential push-pull method, and phase difference method and controls the second actuator on the basis of the tracking error signal.
In addition, a position control apparatus of an optical system according to a third aspect of the present invention comprises an optical system forming a near-field with an optical storage medium and irradiating a converging light beam to the optical storage medium, wherein an objective lens converging the light beam to be irradiated to the optical storage medium and a solid immersion lens with an electrode formed on a surface facing the optical storage medium and irradiating the light beam converged by the objective lens to the optical storage medium are fixed by a holding means, a first actuator for moving the holding means in the focus direction perpendicularly intersecting the storage surface of the optical storage medium, a second actuator for moving the holding means in the direction perpendicularly intersecting the signal storage direction on the optical storage medium, a first control circuit for controlling the first actuator on the basis of electrostatic capacitance formed by the electrode and the optical storage medium and of a reflected light from the optical storage medium so that the distance between the solid immersion lens and the optical storage medium is within the region where the near-field is formed, and a second control circuit for controlling the second actuator on the basis of the reflected light from the optical storage medium, a first moving means for moving an optical head carrying at least the optical system, the first actuator, and the second actuator in the direction perpendicularly intersecting the signal storage direction on the optical storage medium, and a second moving means for moving an optical head carrying at least the optical system, the first actuator, and the second actuator in the signal storage direction on the optical storage medium.
The functions of the position control apparatus of an optical system according to the third aspect of the present invention are as follows.
The function of position control of the holding means in the focus direction is the same as the case of the position control apparatus of an optical system in the first embodiment described previously.
In the present position control apparatus of an optical system, furthermore, the optical head can be moved by the first moving means and the second moving means in the direction perpendicularly intersecting the signal storage direction and in the signal storage direction. Therefore, it is possible to access the card shape storage surface of the storage medium.
In addition, a position control method of an optical system according to a fourth aspect of the present invention is a position control method of an optical system controlling the distance between an optical system which forms a near-field with an optical storage medium and irradiates a converging light beam to the optical storage medium and the optical storage medium by moving the optical system in the focus direction perpendicularly intersecting the storage surface of the optical storage medium, which method comprises a step of controlling an actuator for moving a holding means, fixing an objective lens converging the light beam to be irradiated to the optical storage medium and a solid immersion lens with an electrode formed on a surface facing the optical storage medium and irradiating the light beam converged by the objective lens to the optical storage medium, move in the focus direction on the basis of electrostatic capacitance formed by the electrode and the optical storage medium and of a reflected light from the optical storage medium so that the distance between the solid immersion lens and the optical storage medium is within the region where the near-field is formed.
In addition, a position control method of an optical system according to a second aspect of the present invention is a position control method of an optical system controlling the distance between an optical system which forms a near-field with an optical storage medium and irradiates a converging light beam to the optical storage medium and the optical storage medium by moving the optical system in the focus direction perpendicularly intersecting the storage surface of the optical storage medium, the method comprising the steps of controlling a first actuator for moving a holding means, fixing an objective lens converging the light beam to be irradiated to the optical storage medium and a solid immersion lens with an electrode formed on a surface facing the optical storage medium and irradiating the light beam converged by the objective lens to the optical storage medium, move in the focus direction on the basis of electrostatic capacitance formed by the electrode and the optical storage medium and of a reflected light from the optical storage medium so that the distance between the solid immersion lens and the optical storage medium becomes within the region where the near-field is formed and controlling a second actuator and moving the holding means in the radial direction of the optical storage medium on the basis of a reflected light from the optical storage medium.
In addition, a position control method of an optical system according to a third aspect of the present invention comprises a position control method of an optical system controlling the distance between an optical system which forms a near-field with an optical storage medium and irradiates a converging light beam to the optical storage medium and the optical storage medium by moving the optical system in the focus direction perpendicularly intersecting the storage surface of the optical storage medium, the method comprising the steps of controlling a first actuator for moving a holding means, fixing an objective lens converging the light beam to be irradiated to the optical storage medium and a solid immersion lens with an electrode formed on a surface facing the optical storage medium and irradiating the light beam converged by the objective lens to the optical storage medium, move in the focus direction on the basis of electrostatic capacitance formed by the electrode and the optical storage medium and of a reflected light from the optical storage medium so that the distance between the solid immersion lens and the optical storage medium is within the region where the near-field is formed, moving an optical head carrying at least the optical system, the first actuator, and a second actuator in the direction perpendicularly intersecting the signal storage direction on the optical storage medium, and moving an optical head carrying at least the optical system, the first actuator, and the second actuator in the signal storage direction on the optical storage medium.
In addition, a storage and reproduction apparatus according to a first aspect of the present invention comprises a light source, an optical system forming a near-field with an optical storage medium and irradiating a converging light beam to the optical storage medium, wherein an objective lens converging the light beam to be irradiated to the optical storage medium and a solid immersion lens with an electrode formed on a surface facing the optical storage medium and irradiating the light beam converged by the objective lens to the optical storage medium are fixed by a holding means, an actuator for moving the holding means in the focus direction perpendicularly intersecting the storage surface of the optical storage medium, a control circuit for controlling the actuator on the basis of electrostatic capacitance formed by the electrode and the optical storage medium and of a reflected light from the optical storage medium so that the distance between the solid immersion lens and the optical storage medium is within the region where the near-field is formed, a motor for rotating the optical storage medium when storing information and reproducing information, an intensity modulation circuit for modulating the intensity of the light from the light source according to the information to be stored when storing information, and an information detection circuit for detecting the stored information from the reflected light reflected by the optical storage medium when reproducing information.
In addition, a storage and reproduction apparatus according to a second aspect of the present invention comprises light source, an optical system forming a near-field with an optical storage medium and irradiating a converging light beam to the optical storage medium, wherein an objective lens converging the light beam to be irradiated to the optical storage medium and a solid immersion lens with an electrode formed on a surface facing the optical storage medium and irradiating the light beam converged by the objective lens to the optical storage medium are fixed by a holding means, a first actuator for moving the holding means in the focus direction perpendicularly intersecting the storage surface of the optical storage medium, a second actuator for moving the holding means in the radial direction of the optical storage medium, a first control circuit for controlling the first actuator on the basis of electrostatic capacitance formed by the electrode and the optical storage medium and of a reflected light from the optical storage medium so that the distance between the solid immersion lens and the optical storage medium is within the region where the near-field is formed, a second control circuit for controlling the second actuator on the basis of the reflected light from the optical storage medium, a motor for rotating the optical storage medium when storing information and reproducing information, an intensity modulation circuit for modulating the intensity of the light from the light source according to the information to be stored when storing information, and an information detection circuit for detecting the stored information from the reflected light reflected by the optical storage medium when reproducing information.
In addition, a storage and reproduction apparatus according to a third aspect of the present invention comprises a light source, an optical system forming a near-field with an optical storage medium and irradiating a converging light beam to the optical storage medium, wherein an objective lens converging the light beam to be irradiated to the optical storage medium and a solid immersion lens with an electrode formed on a surface facing the optical storage medium and irradiating the light beam converged by the objective lens to the optical storage medium are fixed by a holding means, a first actuator for moving the holding means in the focus direction perpendicularly intersecting the storage surface of the optical storage medium, a second actuator for moving the holding means in the direction perpendicularly intersecting the signal storage direction on the optical storage medium, a first control circuit for controlling the first actuator on the basis of electrostatic capacitance formed by the electrode and the optical storage medium and of a reflected light from the optical storage medium so that the distance between the solid immersion lens and the optical storage medium is within the region where the near-field is formed, a second control circuit for controlling the second actuator on the basis of the reflected light from the optical storage medium, a first moving means for moving an optical head carrying at least the optical system, the first actuator and the second actuator in the direction perpendicularly intersecting the signal storage direction on the optical storage medium, a second moving means for moving an optical head carrying at least the optical system, the first actuator, and the second actuator in the signal storage direction on the optical storage medium, a motor for rotating the optical storage medium when storing information and reproducing information, an intensity modulation circuit for modulating the intensity of the light from the light source according to the information to be stored when storing information, and an information detection circuit for detecting the stored information from the reflected light reflected by the optical storage medium when reproducing information.